Sound transmission through windows is one of the major noise sources in rooms. The challenge for noise transmission control through a window is in the implementation of any noise control techniques that do not sacrify the vision quality of the window, and are economical enough for mass production. In order to reduce noise transmission, grid-stiffened single-leaf windows are used, however, the use of grid-stiffeners will affect the vision quality of the windows. Some other techniques associating with noise reduction using acoustic resonators are also developed.
European patent to Serge and Eric (E. P. Pat No. 698753), discloses a sliding casement window which has a frame with inner and outer peripheral walls delimiting an inner free space and a peripheral opening. An acoustic resonator unit is disposed in this space. In this patent, the acoustic resonator unit is used to absorb the random impinging sound from outside environment and the transmitting sound in the room. However, since the acoustic resonator is only a narrow band noise control device, it cannot be guaranteed to always work at its resonance in this design, resulting in a low efficiency of noise absorption.
As known in the art, double-glazed windows have been also used for reducing noise transmission. Such windows generally comprise a pair of spaced glass sheets which a hermetically sealed together around their peripheral edges to form a dead-air space of chamber therebetween. Through introducing more mechanical filters, the sound insulation property of the double-glazed windows is significantly improved when compared with a normal single-leaf window. However, double-glazed windows are tied with an unacceptable noise transmission in low-frequencies.
Attempts have been also made in the past to overcome this problem. For example, United States patent to Eric et al. (U.S. Pat. No. 6,231,710) discloses a sandwiched cylindrical structure having a noise attenuation property, in which a Helmholtz resonator network is integrated into the sandwiched cylindrical shell to reduce the sound transmission. However, its potential of the Helmholtz resonator network using for noise transmission control in small enclosures like such a small air chamber inside the double-glazed window is limited because the bulb-like Helmholtz resonator will occupy more space and it is difficult to integrate into the windows without affecting the vision quality.
German patent to Jacobus (D.E. Pat. No. 3401996) discloses a sound-insulating double-glazed window having a circumferential acoustic resonator to control noise in low frequencies. The framework of the window consists of two pieces of frames having a U-shaped space in each, which will form the acoustic resonator body when they are connected, and the gap between the two connected frames forms the opening of the resonator. However, assembling such a window is labor-consuming since the framework includes more components than that of a regular double-glazed window, and in fabrication, more attenuation has to be paid on sealing treatments of the two connected frames, which form the acoustic resonator body and any leakage from it can disable the resonator. Moreover, the resonator used in this double-glazed window is actually a circumferential channel having a small gap, thus, the resonance frequencies of this resonator is difficult to design to target to the air-chamber resonances of interest.
It is an object of the present system to overcome the disadvantages and problems in the prior art.